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If we do only TXOP and 4 AC categories described in my previous posting, it
will correspond to WME, which is another draft for QoS, implemented in some
cards. Let's move on with TGe.
It defines 16 Traffic Identifiers (TID) per destination address (DA). This
defines 16 independent streams simultaneously maintained. From these 16
TID's, first 8 corresponds to 802.1d user priority and are statically mapped
to 4 AC in this way:
TID AC
1(BK) 1(AC_BK)
2 1(AC_BK)
0(BE) 0(AC_BE)
3(EE) 0(AC_BE)
4(CL) 2(AC_VI)
5(VI) 2(AC_VI)
6(VO) 3(AC_VO)
7(NC) 3(AC_VO)
Other 8 TID's, 8-15, used to describe Traffic Streams (TS), and used to
implement IntServ like QoS.
To remind, access to the channel is per AC, with parameters dictated by AP. AP
may change these parameters in run time.
Mechanics of EDCA parameters propagation and other details:
EDCA parameters (CWmin,CWmax,AIFSN,TXOP) included in beacon frame transmitted
by AP periodically (every 100ms). TID included in each frame, there is
special QoS field in 802.11 MAC header. How to distribute per AC time between
TID's is not specified by standard. STA should specify its QoS capabilities
when associating with AP. AP may reject STA that not support QoS. AP may
analyze STA's behavour and disassociate it for protocol violation like over
utilization of channel.
To summarize, this defined diffserv QoS with parameters dictated by AP.
In next post, I will describe HCCA (hybrid coordinated channel access) and
IntServ like QoS.
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